The present invention relates to wheat gluten possessing a fibrous structure and a method for the preparation thereof. More particularly, the invention relates to gluten possessing a fibrous structure to be incorporated in meat-like and fish-like products.
Gluten occurs in nature in combination with carbohydrates and small amounts of lipids and minerals. It is considered as a concentrated natural cereal protein having a bland taste and aroma. It consists mainly of gliadin (prolamine) and glutenin (glutelin), and is mainly used in the bakery industry. The relation of gliadin to glutenin and the influence of ratio of the respective amounts of these two proteins in flour, upon baking quality, have been the subject of numerous investigations.
Increasing attention is now given to the gliadin fraction of gluten. It has been stated that the peculiar properties of gliadin may be due to the hydrogen bonding between the amide groups present in the side chains of the amino acids constituents of this fraction, leading to considerable cross-linking between protein melecules. This is also manifested by the distinctive spongy structure of gliadin. However, the intramolecular bonds in gluten are complex and far from the above scenario, and probably many forces are in play besides hydrogen bonding and disulfide bonds, the latter being considered to exist between the cysteine residues.
U.S. Pat. No. 4,238,515 describes a novel physical form of gluten possessing a net-like fibrous structure being produced by agitating wheat gluten with a reducing agent at a temperature below 70.degree. C. The preferred reducing agents suggested are sodium sulfite and sodium bisulfite. The novel physical form of gluten is mentioned to be most useful as a self-binder in analog-meat products and also as an extender for meat.
In the last few years the Food and Drug Administration (FDA) has reported a number of documents on the problem of the safety of sulfiting agents. As known, sulfiting agents (sodium or potassium salts of sulfite, bisulfite and metabisulfite) are effective in preventing food discoloration due to enzymatic browning. They also serve as microbial growth antagonists and are used to extend the shelf life of fresh cut fruits and vegetables. In 1983, the FDA announced that it had received reports of about 90 cases of adverse reactions (including one death) allegedly caused by ingestion of sulfites in foods.
In addition to the above U.S. Patent which seems to be the most pertinent prior art, there are other patents dealing with protein-based meat-like products having a fibrous structure. Thus according to U.S. Pat. No. 3,197,310, meat-like products having a fibrous structure are obtained by mixing gluten with defatted oil and seed flour and heating at 115.degree. C. The main disadvantage of this process is the denaturation of the protein which occurs at the relatively high temperature employed.
According to U.S. Pat. No. 3,047,395, elastic fibers of a meat-like texture can be obtained from soy flour mixed with water which is heated under pressure. U.S. Pat. No. 3,645,747 describes a method for coagulation of gluten to produce meat-like products having filaments and extended cellular structure wherein heat is used to fix permanently the fibrous structure. However, this method does not allow formation of the heated matrix into meat-like products.
It is interesting to note U.S. Pat. No. 3,409,440 which describes the formation of a stable froth by heating gluten with ascorbic acid, water and glycerin.
U.S. Pat. No. 4,125,630 deals with pliable fibrous texture vegetable protein and meat analogs formulated therewith. It is pointed out in this document that heating to an elevated temperature is absolutely required.
In a very recent U.S. Pat. No. 4,615,901, entitled "Process for separating food stuff having fiber structure" in which wheat gluten is used, temperatures in the range of 75.degree. to 120.degree. C., are claimed. It is specifically stipulated that at temperatures below 75.degree. C., it is difficult to get a sufficient fiber structure. This might explain why the heating was suggested, although heating does involve some denaturation of protein.